The fan blades of a bypass turbojet can be made of composite material, i.e. material made up of synthetic fibers coated in resin. It is desired to be able to perform non-destructive and systematic inspection on all such blades. The materials used have led to X-ray tomography being selected as the most suitable non-destructive inspection method.
For example, U.S. Pat. No. 6,041,143 describes non-destructive inspection of such a fan blade by tomography. The tomographic reconstruction process is associated with the structure of the fiber mass, and in particular is constituted by plies of a sheet material. In that document, the tomographic reconstruction is adapted as a function of the plies. More precisely, at least one reference ply of a reference model is stored in a non-Euclidean coordinate system, and then when inspecting a real blade, the points of the reference ply are transformed into a system of Euclidean coordinates for the real item. This double transformation serves to show up more clearly defects that are specific to blades of that type in which the fiber mass is constituted by plies in a sheet material, in particular defects constituted by the formation of wrinkles.
The invention relates to non-destructive tomographic inspection of blades of another type that comprises a blank or preform made out of yarns or fibers woven in three dimensions. Such a blank is embedded in resin. For example, patent EP 1 526 285 in the name of the Applicant describes a blade of this kind.
During the process of fabricating this type of blade, various defects can occur. Non-destructive tomographic inspection is used to detect and evaluate such defects.
One specific defect is the formation of clumps of resin within the structure. To detect and evaluate these defects, it is necessary to calibrate the tomographic installation regularly using a test blade, and in particular one that includes such clumps of resin, that are of dimensions that are known, and that are situated at locations that are known.
The invention relates to making such a test blade.